The invention is generally related to the field of semiconductor devices and more specifically to isolating exposed conducting surfaces in semiconductor devices.
As the density of semiconductor devices increases, the demands on interconnect layers for connecting the semiconductor devices to each other also increases. Therefore, there is a desire to switch from the traditional aluminum metal interconnects to copper interconnects. Unfortunately, suitable copper etches for a semiconductor fabrication environment are not readily available. To overcome the copper etch problem, damascene processes have been developed.
In a conventional interconnect process, the aluminum (and any barrier metals) are deposited, patterned, and etched to form the interconnect lines. Then, an intrametal dielectric (IMD) is deposited and planarized. In a damascene process, the IMD is formed first. The IMD is then patterned and etched. The barrier layer and a copper seed layer are then deposited over the structure. The copper layer is the formed using the seed layer over the entire structure. The copper is then chemically-mechanically polished (CMP""d) to remove the copper from over the IMD 16, leaving copper interconnect lines 18 as shown in FIG. 1A. A metal etch is thereby avoided.
Next, a silicon nitride layer 20 is deposited over the copper 18 and IMD 16, as shown in FIG. 1B. Copper must be surrounded by a barrier to prevent it from diffusing into the surrounding dielectric. An interlevel dielectric (ILD) 22 is then formed over the silicon nitride layer 20. Unfortunately, the silicon nitride layer increases the line-to-line capacitance by increasing the total effective dielectric constant of the interievel dielectric (ILD 22 and silicon nitride 20). Silicon nitride 20 also takes up voluble space that is needed for other essential device components.
The invention forms a thin aluminum-oxide on the surface of an exposed conducting surface. A selective aluminum deposition is used to deposit aluminum only on the conducting surface and not on the surrounding dielectric. The aluminum is then oxidized to form an isolation layer.
An advantage of the invention is providing an isolating film on a conducting surface but not a surrounding dielectric to minimize the space taken by the isolating film and/or reduce the effective dielectric constant.
This other advantages will be apparent to those of ordinary skill in the art having reference to the specification in conjunction with the drawings.